This invention relates to catalytic hydrocarbon processing, and particularly to hydrocarbon hydroprocessing, such as the process involving catalyzing the reaction of hydrogen with organosulfur, organonitrogen, and organometallic compounds. More particularly, this invention is directed to a process for hydrodemetallizing hydrocarbon liquids.
During the course of a typical process involving the catalytic refining of hydrocarbons, portions of contaminant metals and sulfur components contained in a hydrocarbon oil ordinarily are deposited on a porous particulate catalyst, causing a loss of catalytic activity and stability. Residual petroleum oil fractions, such as the heavy fractions produced in atmospheric and vacuum crude distillation columns, are especially undesirable as feedstocks for such catalytic refining processes due to their high contaminant metals and/or sulfur content. Economic considerations have recently provided new incentives for catalytic conversion of the heavy fractions to more marketable products. However, the presence of high concentrations of sulfur and contaminant metals precludes the effective use of residua as feedstocks for cracking, hydrocracking, and similar catalytic refining operations.
Methods are available to reduce the sulfur and metals content of residua. One such method is hydrodesulfurization, a process wherein a residuum contacts a catalyst usually containing hydrogenation metals on a porous refractory oxide support under conditions of elevated temperature and pressure and in the presence of hydrogen, such that sulfur components are converted to hydrogen sulfide, nitrogen components are converted to ammonia, while the contaminant metals are simultaneously deposited on the catalyst. The most common contaminant metals found in such hydrocarbon fractions include nickel, vanadium and iron. The extent of deactivation of the catalyst typically is a function of the amount of deposition of contaminant metals on the catalyst surface and in its pores, i.e., the usefulness of the catalyst steadily decreases as the amount of deposited metals increases with continued treatment of the residuum. Increased metals deposition as well as high coke deposition, may cause plugging of catalyst beds resulting in premature replacement of catalyst beds in the hydrocarbon refining reactors.
It has been recognized that hydrodesulfurization of hydrocarbons may involve removing a substantial proportion of contaminant metals prior to downstream removal of sulfur and nitrogen. For example in U.S. Pat. No. 4,431,526, contaminant metals are removed by contact with a relatively large pore first catalyst and then sulfur and additional contaminant metals are subsequently removed by a relatively small pore downstream catalyst. Another typical example of a demetallization process is disclosed in U.S. Pat. No. 4,548,710 wherein a relatively large pore demetallization catalyst accumulates (deposits) its own fresh weight in contaminant metals. Such a demetallization process allows the refiner to subsequently pass a feedstock having a substantially reduced metals content over a high surface area desulfurization catalyst such as that prepared in accordance with U.S. Pat. No. 3,980,552.
Catalytic removal of metals from hydrocarbons involving multiple reaction zones provides only limited improvement to such problems as catalyst activity before undesirable characteristics such as catalyst stability (i.e. catalyst life) are adversely affected. A need still exists for an improved process for depositing contaminant metals on a particulate catalyst.
It is, therefore, a major object of the present invention to provide a process for removing contaminant metals from a hydrocarbon oil, and more specifically to provide a catalytic hydrodemetallization process while simultaneously removing a substantial proportion of sulfur and Conradson carbon from a hydrocarbon oil.
It is another object of the invention to provide a multi-reaction zone process for the catalytic hydrodemetallization of a hydrocarbon oil, and more specifically to provide a process for substantially hydrodemetallizing a heavy hydrocarbon oil prior to substantially hydrodesulfurizing the oil.
A further object of the invention is to provide hydrocarbon products of reduced metals content so as to extend the life of downstream refining catalysts.
These and other objects and advantages of the invention will become apparent from the following description.